1. Field of the Invention
The present invention relates to a method and an apparatus for printing, in which a detect of an image due to faulty nozzle causing fluctuation or failure in ejection, can be complemented.
2. Description of the Related Art
An ink-jet type printing method is adapted to form an image of a printing medium by directly ejecting ink droplets onto the printing medium through a printing head located in opposition to the printing medium with a predetermined clearance. Different from electrophotographic or laser printing method or so forth, there are much lesser process and/or components required in formation of the image. Therefore, desired image can be stably obtained.
However, in the ink-jet printing method, there is an instability factor for formation of an image by ejecting fine ink droplets through ends (ejection openings) of a plurality of fine nozzles of a printing head. A phenomenon representative of such instability is fluctuation or failure in ejection for example. Failure of ejection can be caused by stopping the flow in the nozzle due to dust, ink of increased viscosity and so forth, breakage of heater in the nozzle, covering of the ejection opening of the nozzle by the ink droplet and so forth. Therefore, if ejection failure is caused in a part of the nozzles among a plurality of nozzles in the printing head, when the printing head is driven in a primary scanning direction with respect to the printing medium, a white line extending in the primary scanning direction should appear at the position of the printing medium corresponding to the faulty nozzles not ejecting the ink. Conventionally, once failure of ejection is caused in the printing head, it has been not possible to obtain an image having no defect.
The possibility of occurrence of failure in ejection is progressively increased in proportion to an increasing number of nozzles. Therefore, when the number of nozzles is increased to be several hundreds or several thousands for the purpose of speeding of printing, possibility of occurrence of the faulty nozzle is proportionally.increased. This makes it difficult to achieve high speed printing without causing defect on the printed image,
On the other hand, in viewpoint of manufacturing of the printing head, conventionally, it is inherently required to produce the defect free printing heads, all of the nozzle of which are in normal condition. Thus, increasing of number of nozzles to be provided in one printing head should result in increasing of possibility of defects in the printing head and thus inherently results in lowering of yield in manufacturing. This inherently raises production cost of the printing head.
Furthermore, even when a defect free printing head is successfully produced, if failure of the nozzle is caused during use to.make ink ejection through such faulty nozzle unstable to degrade the obtained image. Therefore, such printing head with faulty nozzle becomes not possible to use and has to be exchanged. On the other hand, in four to eight color ink-jet printing apparatus employing four to eight printing heads, each having several thousands of nozzles, if failure is caused in one or more nozzles, defective print is produced at every time of occurrence of failure. Furthermore, at every occurrence of failure, the printing head has to be exchanged to inherently stop the overall printing apparatus. Therefore, the apparatus becomes not possible to operate stably.
As a solution for this, the applicant has proposed a printing method and a printing apparatus which can perform complementing printing for obtaining complete printing products even in presence of the faulty nozzle in the printing head, in Japanese Patent Application Laying-open No. 25700/1996. Namely, the proposed printing method performs auxiliary scanning for the printing medium by an auxiliary scanning means for a magnitude smaller than an arrangement length of printing elements (nozzles) in the printing head after completion of primary printing scan by a primary scanning means with shifting of the printing head relative to the printing medium, so that the complemental printing for the printing region where printing has not been performed in the preceding primary scanning cycle due to failure of the printing element with other printing element during returning of the printing head to an initial position for the next primary scanning operation.
With such innovative printing method, the non-printed portion can be complementally printed so that a complete printing product can be obtained even when the faulty nozzle is present in the printing head.
However, such printing method still maintains rooms for improvement as claimed below.
(1) It is inherent to change flow of complemental printing when non-printing failure is caused on the nozzle located at certain positions among a plurality of nozzles in the printing head. For instance, when the faulty nozzle is located at a lower end of an array of a plurality nozzles in the auxiliary scanning direction, complemental print for a complementally printing defect caused by such faulty nozzle cannot be performed by a flow for complementally printing adapted for shifting in the downstream side in the auxiliary scanning direction. Therefore, in such case, the flow has to be changed to a flow for causing shift in the upstream side.
(2) On the other hand, the width of the image corresponding to the width of the array of the nozzles in the printing head is varied. The auxiliary scanning width for complementally printing is also varied. Therefore, the data unit of the image to be handled is varied.
(3) Since feeding amount in the auxiliary scanning direction for complementally printing is not constant.
(4) There are the foregoing problems in the items (1) to (3) which are mutually correlated to obtain satisfactory or complete complemental function, when the principle of complemental printing is applied for a color printing apparatus having a plurality of printing heads.
(5) It is difficult to accurately perform auxiliary scan of the printing medium in the extent corresponding to one or several pixels. Particularly, in case of a large scale apparatus, such as a printing apparatus performing textile printing in ink-jet system, in which a construction for transporting a cloth as the printing medium with an endless belt of about 1.8 m width becomes necessary. It is quite difficult or even impossible to provide a fine shift in the extent of several tens xcexcm corresponding to one pixel. If overrunning is caused by excessive shift of the printing medium, it has been necessary to stop at the target position by several times of reciprocating shift, or to shift in large extent back to the original position to again shift for one pixel to reach the target position. Thus, feeding operation for complementing printing becomes too complicate.
In a first aspect of the present invention, there is provided a printing apparatus, comprising:
primary scanning means for performing primary scan of a printing head relative to a printing medium, the printing head having a plurality of printing elements arranged;
printing head driving means for driving the printing elements of the printing head, during primary scan of the printing head by the primary scanning means, to form an image on the printing medium;
auxiliary scanning means for performing auxiliary scanning of the printing head in a direction substantially perpendicular to the scanning direction of the primary scanning means, relative to the printing medium; and
printing control means, at a printing region of the printing medium corresponding to the printing element of the printing head which cannot perform printing in a forward direction of the primary scan, for performing complementally printing by another printing element in a condition where the printing head and the printing medium are relatively shifted in the direction of auxiliary scan at least a pitch between the printing elements of the printing head, and then performing next printing in a condition where the shifting of the printing head and the printing medium in the direction of the auxiliary scan be eliminated.
Here, it may further comprise shifting means for shifting the printing head relative to the printing head in the auxiliary scanning direction, wherein the shifting of the printing head in the auxiliary scanning direction, wherein the shifting of the printing head in the auxiliary scanning direction depending upon the pitch between the printing elements is performed by the auxiliary scanning means.
According to the above invention, it is possible to perform a printing head in the auxiliary scanning direction by only a predetermined fine distance. Therefore, a non-printed portion on the printing medium caused by the faulty nozzle of the printing head can be accurately printed by the other normal nozzle without any failure, and a defect image including the non-printed portion can be complemented.
In the above invention, the printing elements of the printing head may be arranged along the auxiliary scanning direction. The printing head may also perform printing in a width corresponding to a length of a printing element array excluding at least one of opposite ends of the array of the printing elements.
According to the above invention, even when the faulty causes at a printing element positioned at ends of the array of the printing elements, it is possible to accurately shift the printing head in the auxiliary scanning direction, and accordingly the defect image including the non-printed portion of the printing medium caused by an abnormal printing element on a forward primary scan can correspond to the normal printing element of the printing head. Therefore, the non-printed portion can be complementally printed on a backward primary scan by the other normal printing element.
In the above invention, it may further comprise abnormality detecting means for detecting an abnormal printing element among printing elements of the printing head. The printing head may have ink ejection openings for ejecting ink corresponding to the plurality of printing elements, and within each of the ejection openings, ejection means for ejecting ink is provided.
According to the present invention, abnormality of the printing element can be rapidly detected. Therefore, complement of defect image on the printing medium caused by the abnormal printing element can be smoothly performed.
In the above invention, the ejection means may be an electrothermal energy transducer applying a thermal energy for the ink, and causing state variation is the ink by the heat for ejection of the ink. A cloth may be used as the printing medium.
In a second aspect of the present invention, there is provided a printing apparatus including:
primary scanning means for performing primary scan of a printing head relative to a printing medium, the printing head having a plurality of printing elements arranged;
printing head driving means for driving the printing elements of the printing head, during primary scan of the printing head by the primary scanning means, to form an image on the printing medium; and
auxiliary scanning means for performing auxiliary scanning of the printing head in a direction substantially perpendicular to the scanning direction of the primary scanning means, relative to the printing medium,
the printing method, comprising the steps of:
printing with excluding a printing element which caused failure, among a plurality of printing elements upon printing scan in a forward direction by the printing head driven for the primary scanning;
shifting the printing head relative to the printing medium in the direction of auxiliary scan at least a pitch between the printing elements of the printing head, after the previous printing step is performed;
complementally printing at a printing region of the printing medium corresponding to the printing element of the printing head which cannot perform printing in a forward direction of the primary scan, by another printing element in a condition where the printing head and the printing medium are relatively shifted by the previous shifting step; and
eliminating the shift in the auxiliary scanning direction between the printing head and the printing medium for next printing scan.
Here, the shifting of the printing head in the auxiliary scanning direction depending upon the pitch between the printing elements, may be performed by the auxiliary scanning means.
According to the present invention, the defect image generated by abnormal printing element detected at the detection step can be complementally printed after shifting the printing head relative to the printing medium in the auxiliary scanning direction at the auxiliary scanning step. In this case, since the shift can be more accurately performed than a case the printing medium is shifted, the complement of the defect image can be easily performed. In order to complement the defect image on the printing medium, only the printing head is scanned in the auxiliary scanning direction, and the printing medium is however scanned in the auxiliary scanning direction only the case where the usual printing is performed. Therefore, shift of the printing medium is always constant.
In the above invention, the printing step may be performed on the basis of an image data excluding image data segment corresponding to a faulty printing element when failure caused on the faulty printing element is not non-ejecting failure.
When the faulty of the abnormal printing element is non-ejection, a white line as non-printed portion is formed. According to the above invention, even if the faulty of the abnormal printing element is not non-ejection, the white line can be formed on the printing medium by excluding image data segment corresponding to the faulty printing element. Therefore, the flow of the complemental printing step can be performed at a constant, and the apparatus becomes simple.
In the above invention, the complemental printing step may be performed by reading out an image for the faulty printing element excluding in the printing scan in forward direction.
According to the above invention, since the defect image generated on the forward primary scan can be complementally printed on the backward primary scan, it is possible to prevent ink from overlapping on the printing medium.
In the above invention, the shifting step may include judgment step after providing shift in the auxiliary scanning direction for the printing head, the judgment step for making judgment whether other printing element in failure is opposed to the printing region on the printing medium corresponding to the faulty printing element of the printing head which cannot perform printing the printing scan in the forward direction.
According to the above invention, it is possible to check the normal printing element faces to the defect image as non-printed portion of the printing medium by fine shifting in the auxiliary scanning direction. Furthermore, it is possible to certainly judge the possibility of the complemental printing.
In the above invention, the complemental printing step is performed according to the judgment step when ink ejection is possible for the printing region on the printing medium corresponding to the faulty printing element of the printing head which cannot perform printing the printing scan in the forward direction.
The complemental printing step may be stopped on the basis of the judgment step when ink ejection is not possible for the printing region on the printing medium corresponding to the faulty printing element of the printing head which cannot perform printing the printing scan in the forward direction.
Stopping of the complemental printing step may be followed by a warning.
The complemental printing step may be further performed when ink ejection is not possible for the printing region on the printing medium corresponding to the faulty printing element of the printing head which cannot perform printing the printing scan in the forward direction.
The printing head may have ink ejection openings for ejecting ink corresponding to the plurality of printing elements, and within each of the ejection openings, ejection means for ejecting ink is provided.
The ejection means may be an electrothermal energy transducer applying a thermal energy for the ink, and causing state variation in the ink by heat for ejection of the ink.
A cloth may be used as the printing medium.
According to the above invention, since the simple flow for complement of the defect image is employed, even if any of ejection means as a plurality of printing elements causes the fault such as poor-ejection or non-ejection failure, a non-printed portion on the printing medium can be printed by a normal printing element, and an image defect caused by such failure can be complemented to obtain an high definition image.
In a third aspect of the present invention, there is provided a printing apparatus, comprising:
primary scanning means for performing primary scan of a printing head relative to a printing medium, the printing head having a plurality of printing elements arranged;
printing head driving means for driving the printing elements of the printing head, during primary scan of the printing head by the primary scanning means, to form an image on the printing medium;
shifting means for shifting the printing head in a direction substantially perpendicular to the scanning direction of the primary scanning means, relative to the printing medium; and
printing control means, at a printing region of the printing medium corresponding to the printing element of the printing head which cannot perform printing in a forward direction of the primary scan, for performing complementally printing by another printing element in a condition where the printing head and the printing medium are relatively shifted by the shifting means at least a pitch between the printing elements of the printing head, and then performing next printing in a condition where the shifting of the printing head and the printing medium in the direction of the auxiliary scan be eliminated.
In a fourth aspect of the present invention, there is provided a printing method in a printing apparatus including:
primary scanning means for performing primary scan of a printing head relative to a printing medium, the printing head having a plurality of printing elements arranged;
printing head driving means for driving the printing elements of the printing head, during primary scan of the printing head by the primary scanning means, to form an image on the printing medium; and
shifting means for shifting the printing head in a direction substantially perpendicular to the scanning direction of the primary scanning means, relative to the printing medium;
the printing method, comprising the steps of:
printing with excluding a printing element which caused failure, among a plurality of printing elements upon printing scan in a forward direction by the printing head driven for the primary scanning;
shifting the printing head relative to the printing medium by the shifting means at least a pitch between the printing elements of the printing head, after the previous printing step is performed;
complementally printing at a printing region of the printing medium corresponding to the printing element of the printing head which cannot perform printing in a forward direction of the primary scan, by another printing element in a condition where the printing head and the printing medium are relatively shifted by the previous shifting step; and
eliminating the shift in the auxiliary scanning direction between the printing head and the printing medium for next printing scan.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.